Product failure / guarantee

I own several pairs of Crocs foot wear and have been happy with the quality. I bought a pair of men's rubber slipons during 2017 at Crocs in Somerset Mall in Somerset West. I have worn them about 6 months at home and going out. No heavy terrain or heavy wearing. I have an old pair that I wear for that purpose. The V that covers the foot is glued to the strap between the toes. This connection has come undone. I took the slipons and went back to the store in Somerset Mall expecting to have the slipons replaced because of a manufacturing defect. I was told I need to bring the cash slip or bank statement indicating and verifying the purchase. I haven't kept the slip, just as I discard slips of all other items of whatever kind I buy. I am sure normal legal warranty applies in this case. I am also of the opinion that customer satisfaction is important to manufacturers. I would like Crocs to either repair the slipon or replace.